The United States Department of Energy (DOE) National Energy Technology Laboratory (NETL) conducts programs that support the global interest for clean power generation such as the Turbine, Program. In support of the goals of the Turbine Program, researchers at NETL are developing sensor technology for combustion monitoring and control. This sensor development is based on using the flame's electrical properties to perform real-time diagnostics and in-situ monitoring of critical combustion parameters as set forth in Thornton, J., Richards, G.A., and Robey, E., “Detetcing Flashback in Premix Combustion Systems” presented at the American Flame Research Comittee International Symposium, Newport Beach, Calif., 2000, the disclosure of which is incorporated by reference.
It is well known that a flame can conduct electrical current as set forth in Thornton, J. D., Straub, D. L., Richards, G. A., Nutter, R. S., Robey, E., “An In-Situ Monitoring Technique for Control and Diagnostics of Natural Gas Combustion Systems,” the 2nd Joint Meeting of the U.S. Sections of the Combustion Institute, Oakland, Calif., Mar. 25-28, 2001, the disclosure of which is incorporated by reference, and that the measured current conducted through the flame relates to the flame characteristics. The flame ionization detector (FID) used in gas chromatography uses the measured current through the flame to measure very low concentrations of hydrocarbons. The reaction most often cited for providing the FID response results from the chemi-ionization of CHO:CH+O→CHO*→CHO++e−  (1)
Application of sufficient voltage allows complete collection of the generated electrons. The number of electrons produced has been found to be proportional to the number of hydrocarbons in the sample, with modifications for specific functional groups such as —OH.
To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented which operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blowoff, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio, see U.S. Pat. No. 6,429,020 issued to Thornton et al. Aug. 6, 2002, incorporated herein by reference, and a paper by Thornton, J. D., Straub, D. L., Richards, G. A., Nutter, R. S., Robey, E., “An In-Situ Monitoring Technique for Control and Diagnostics of Natural Gas Combustion Systems,” the 2nd Joint Meeting of the U.S. Sections of the Combustion Institute, Oakland, Calif., Mar. 25-28, 2001, incorporated by reference herein, and in a patent application filed Sep. 18, 2001 by Thornton et al., U.S. Ser. No. 09/955,582, entitled Real-Time Combustion Control and Diagnostics Sensor (CCADS), the entire disclosure of which is incorporated by reference. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor.
However, pressure oscillations in the combustor result in variations in both the amplitudes and frequencies in the combustion chamber, possibly resulting in adverse consequences. Detecting and controlling the pressure oscillation in real time is a problem not yet solved.